JPH04241328A - Control method for optical amplifier and optical amplifier - Google Patents

Abstract

PURPOSE:To provide the control method for the optical amplifier which eliminates the influence of the natural release light of the optical amplifier without superposing a low-frequency signal on transmission signal light and the optical amplifier. CONSTITUTION:This optical amplifier 100 is constituted by including the optical amplifier 101 and a narrow-band optical filter 104 which is connected behind the optical amplifier 101 and eliminates the natural release light outputted form the optical amplifier 101. The intensity of the light transmitted through the narrow-band optical filter 104 and the intensity of the light reflected by the narrow-band optical filter 104 are compared in a control circuit 113 and the gain of the optical amplifier 101 is controlled. The transmission signal light can control the gain of the optical amplifier without superposing the low- frequency signal thereon. Then, the generation of so-called chirping of the transmission light wavelength by modulation with the low-frequency signal is obviated and the transmission at the correspondingly longer distance is possible.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplification device used in optical communications and the like.

0002

[Prior Art] When using an optical amplifier that directly amplifies light using an optical amplifier as an optical repeater in an optical communication system, it is necessary to keep the output level constant. In this method, the power level is monitored not only of the signal light but also of the spontaneous emission light of the optical amplifier. Therefore,
Conventionally, in order to remove the influence of spontaneous emission light from an optical amplifier, a low frequency signal is superimposed on the transmitted signal light, and the low frequency signal is extracted from the signal obtained by optical/electrical conversion of the branched light output from the optical amplifier. The method used was to extract the signal and monitor the magnitude of the low frequency signal. Regarding this method, for example, "Study of semiconductor laser optical amplifier repeater" by Yamamoto et al.
This is detailed in the paper published in the Proceedings of the 1989 Autumn National Conference of the Institute of Electronics, Information and Communication Engineers, Vol. 4, pp. 4-38.

0003

[Problems to be Solved by the Invention] However, in conventional optical amplification devices, it is necessary to superimpose a low-frequency signal on the transmitted signal light, and the optical frequency of the transmitted signal light is also modulated at the same time by the low-frequency signal superposition, resulting in the so-called Since wavelength chirping occurs, there is a problem in that the influence of wavelength dispersion of the optical fiber increases. The present invention solves the above problems,
An object of the present invention is to provide a control method for an optical amplifying device and an optical amplifying device that eliminate the influence of spontaneous emission light of an optical amplifier without superimposing a low frequency signal on a transmitted signal light.

0004

[Means for Solving the Problems] The present invention provides an optical amplification device including (1) an optical amplifier and a narrowband optical filter that is connected after the optical amplifier and removes spontaneously emitted light output from the optical amplifier. , the gain of the optical amplifier is controlled by comparing the intensity of light transmitted through the narrowband optical filter and the intensity of light reflected by the narrowband optical filter.

(2) having at least three terminals, the first
The light input from the terminal is output from the second terminal, the light input from the second terminal is output from the third terminal, and the optical circulator is connected to the first terminal of the optical circulator. an optical amplifier and a narrowband optical filter connected to a second terminal of the optical circulator, using the output light from the narrowband optical filter and the output light from the third terminal of the optical isolator. It is characterized in that the gain of the optical amplifier is set to a predetermined level.

(3) The light input from the first input/output terminal is output from the second and third input/output terminals, and the light input from the second input/output terminal is output from the first and third input/output terminals. an optical branching element outputted from an input/output terminal of No. 4; an optical isolator connected to the first input/output terminal of the optical branching element in a direction in which light passes; and an optical amplifier connected before the optical isolator. and a narrowband optical filter connected to a second input/output terminal of the optical branching element, the output light from the third input/output terminal of the optical branching element and the fourth input/output terminal of the optical branching element. It is characterized in that the gain of the optical amplifier is set to a predetermined level using the output light from the input/output terminal.

(4) The optical amplifier has an optical amplifier, an optical isolator connected after the optical amplifier, first and second input/output terminals, and a monitor terminal for monitoring input light from the second input/output terminal. a first optical branching element whose first input/output terminal is connected to the optical isolator; a narrowband optical filter connected to a second input/output terminal of the first optical branching element; 1 and a second input/output terminal, and a monitor terminal for monitoring input light from the first input/output terminal;
a second filter whose input/output terminals are connected to the narrowband optical filter;
an optical branching element, and the gain of the optical amplifier reaches a predetermined level using the output light from the monitor terminal of the second optical branching element and the output light from the monitor terminal of the first optical branching element. It is characterized by setting as follows.

(5) An optical amplifier, an optical isolator connected after the optical amplifier, and an optical isolator placed after the optical isolator, in which the reflected light of the light incident on the optical isolator follows an optical path different from the original optical path. and a narrowband optical filter installed at an angle with respect to the incident optical axis, and the gain of the optical amplifier is determined by using the output light from the narrowband filter and the reflected light from the narrowband optical filter. It is characterized in that the level is set to be the same.

[0009]

[Operation] In the present invention, by the means described above, the light reflected by the narrow band optical filter, which contains only the spontaneous emission light component with almost all the signal light component removed, out of the output light from the optical amplifier; First, it is detected whether the optical signal is being input to the optical amplification device from the ratio of the light intensity of the signal light and the light transmitted through the narrowband optical filter, which is composed of the spontaneous emission light component within the transmission bandwidth of the narrowband optical filter. Then, if it is detected that an optical signal is being input, the output light level from the optical amplifier can be controlled to a constant level by monitoring the output light level of the narrowband optical filter. On the other hand, if the gain of the optical amplifier is controlled to be at least below a certain level when the absence of optical signal input is detected, the gain of the optical amplifier can be maintained in an abnormally high state even when the input signal is disconnected. There will be no such situation. Therefore, it is possible to detect whether or not an optical signal is input to the optical amplifier without superimposing a low frequency signal on the transmitted signal light, and stable output control can be performed.

0010

[Examples] The present invention will be explained below with reference to Examples. FIG. 1 is a block diagram of a first embodiment of the present invention, and FIGS. 2 to 4 are explanatory diagrams for explaining the first to fifth embodiments.

In FIG. 1, input signal light 102 is optically amplified by optical amplifier 101 and output as optical amplifier output light 103. Here, the input signal light 102 consists of a spectrum of only the signal light as shown in FIG. 2(a), while the optical amplifier output light 103 consists of an optically amplified signal as shown in FIG. 2(b). It includes light and spontaneous emission light added by the optical amplifier 101. Since this spontaneously emitted light becomes noise in the optical signal, it is desirable to remove it as much as possible. Therefore, the optical amplifier output light 103 is passed through the narrow band optical filter 10.
4 to remove as much spontaneous emission light as possible. This removed spontaneous emission light is filtered through a narrow band optical filter 104.
The reflected light becomes reflected light 105, a part of which is split by a first light splitting mirror 106 and enters a first light receiver 107.

Here, the transmission of the narrow band optical filter 104 /
As shown in FIGS. 3A and 3B, the reflection characteristics are an optical filter with a center wavelength λ and a transmission bandwidth Δλ. Transmission bandwidth △
As λ, for example, a value of several nm is used. Because of such transmission characteristics, the narrow band optical filter 10
As shown in FIG. 2(d), the reflected light 105 from 4 is obtained by excluding some spectral components that pass through the narrowband optical filter 104 from the spontaneous emission spectrum shown in FIG. 2(b). It consists of a spectrum that includes most of the spontaneously emitted light. On the other hand, the transmitted light 1 that has passed through the narrow band optical filter 104
08 includes, in addition to the optically amplified signal light, a part of spontaneously emitted light that has passed through the narrow band optical filter 104, as shown in FIG. 2(c). A part of this transmitted light 108 is branched by a second light branching mirror 109 as branched light 110, and the light intensity thereof is monitored by a second light receiver 111. Most of the transmitted light 108 that passes through the second optical splitting mirror 109 without being split is outputted from the optical amplifier 100 as an output signal light 112.

Here, whether or not the signal light is input to the optical amplifier 101 can be determined from the light amount ratio of the reflected light 105 and the transmitted light 108 monitored by the first optical receiver 107 and the second optical receiver 111. I can do it. For example, as shown in FIG. 4(a), when the input signal light 102 to the optical amplifier 100 is absent or extremely weak, the output light from the optical amplifier 101 is is almost exclusively spontaneously emitted light. Therefore, the transmitted light 108 that has passed through the narrow band optical filter 104 is only a part of spontaneously emitted light that has passed through the narrow pass band, and there is no signal component. At this time, the optical amplifier 1
The spectrum shape of the spontaneous emission light from the optical amplifier 10
The transmitted light 10 when there is no input signal light 102 does not change that much with respect to the change in the excitation level of 1.
8 and the reflected light 105 does not depend much on the excitation level of the optical amplifier 101. Therefore, the presence or absence of the input signal light 102 can be detected by looking at the ratio of the transmitted light 108 and the reflected light 105. As an example of a rough value, for example, if a broadband optical fiber amplifier is used as the optical amplifier 101, the spectral width of spontaneous emission light is approximately 3.
On the other hand, if the bandwidth of the narrowband optical filter 104 is, for example, 3 nm, the intensity ratio of the transmitted light 108 to the reflected light 105 is about 1/9. At this time, if the ratio of the transmitted light 108 to the reflected light 105 is approximately 1/9 or more, it can be determined that the signal light is incident on the optical amplification device 100.

Therefore, the control circuit 113 first detects whether the light intensity ratio of the transmitted light 108 to the reflected light 105 is greater than or equal to a predetermined ratio indicating that the signal light is incident on the optical amplification device 100. However, if the ratio is below a predetermined ratio, no signal light is being incident, and therefore the optical amplifier 101 is controlled so that the excitation level of the optical amplifier 101 becomes a predetermined excitation level. Furthermore, if the ratio is greater than or equal to a predetermined ratio, signal light is incident, so the excitation light level is controlled so that the transmitted light intensity becomes a predetermined constant value. As a result of the above, the optical output level from the optical amplifier device 100 is kept constant when the signal light is incident, and a constant gain state is maintained when the signal light is not incident.

FIG. 5 shows a block diagram of a second embodiment of the present invention. The signal light that has passed through the first optical fiber 501 and entered the optical amplifier 502 is optically amplified and then transferred to the second optical fiber 503.
is output to. As shown in FIG. 2(b), this output light includes spontaneous emission light in addition to optically amplified signal light. The optically amplified signal light that has entered the second optical fiber 503 enters the first terminal 521 of the optical circulator 504, is output from the second terminal 522, and is output to the third optical fiber 506. Of the light incident on the narrow band optical filter 507 from the third optical fiber 506, almost the signal light is output to the fourth optical fiber 508, and the optical amplifier 5
Most of the spontaneous emission light added at step 02 is reflected by the narrow band optical filter 507 and returns to the second terminal 522 of the optical circulator 504, and is output from the third terminal 523 to the fifth optical fiber 509.

FIG. 6 shows the details of the configuration of the narrow band optical filter 507. 1st and 2nd 1/4
Constructed using pitch rod lenses 601 and 602 and a dielectric multilayer filter 603, the dielectric multilayer filter 6
Approximately 1/4 pitch rod lens 601, 60 of 03 surface
It almost coincides with the direction of the central axis of 2. Therefore, the spontaneous emission light component reflected by the dielectric multilayer filter 603 as shown in FIG. The light is then outputted to the fifth optical fiber 509 through the third terminal, and finally received by the first light receiver 510.

On the other hand, FIG. 2(c) (when there is signal light) or FIG. 4(c)(
When there is no signal light), the light with the spectrum shown in Fig. 5 is output to the fourth optical fiber 508, further passes through the optical branching element 511, and 98% of the light is transmitted to the sixth optical fiber 512.
is output to. Furthermore, the remaining 2% of the light that enters the optical branching element 511 from the fourth optical fiber 508 is branched and passes through the seventh optical fiber 513 to the second optical receiver 51.
The light is received at 4.

Here, monitor signals for the amount of light received by the first optical receiver 510 and the second optical receiver 514 are input to a control circuit 515, and based on these signals, the optical amplifier 5
02 gain is controlled. The control process is the same as in the first embodiment, and will be omitted here.

A feature of this configuration is that most of the reflected light from the narrow band optical filter can be received by the first light receiving element. Furthermore, since the optical branching element is used only at a location for monitoring the final output light, the branching ratio can be increased, and the loss of the amplified signal light is small.

FIG. 7 shows a block diagram of a third embodiment of the present invention. The signal light that has passed through the first optical fiber 701 and entered the optical amplifier 702 is optically amplified and then transferred to the second optical fiber 703.
is output to. As shown in FIG. 2(b), this output light includes spontaneous emission light in addition to optically amplified signal light. The optically amplified signal light that entered the second optical fiber 703 enters the first terminal 721 of the optical isolator 704,
The signal is output from the second terminal 722 and is output to the third optical fiber 705. The direction of isolation of this optical isolator is such that light incident from the first terminal 721 passes through the optical isolator, and light traveling from the second terminal 722 to the first terminal 721 is not transmitted. Now, the light input to the third optical fiber 705 is input to the first terminal 731 of the optical branching element 706, and 90% of the light is output from the second terminal 732 to the fourth optical fiber 707. It is input to bandpass optical filter 708 . Also, the remaining 1
0% light is transmitted from the third terminal 733 to the fifth optical fiber 70
9 and is received by a second optical receiver 710, and the level of output light from the optical amplifier 702 is monitored. Note that the configuration of the narrow band optical filter 708 used here is the same as in the first embodiment, as shown in FIG.

Of the light input from the fourth optical fiber 707 to the narrow band optical filter 708, the spontaneous emission light component with the spectrum shown in FIG.
and is output to the fourth optical fiber 707 from which it came. This light enters the optical branching element 706 again from the second terminal, and 10% of the light is output from the fourth terminal and input into the sixth optical fiber 712, and then passes through the first light receiver 713.
The light is received by Based on the amount of light received, the optical amplifier 70
The spontaneous emission light amount of 2 is monitored. Also, of the light input from the fourth optical fiber 707 to the narrowband optical filter 708, the spectra shown in FIG. 2(c) (when there is signal light) and FIG. 4(c) (when there is no signal light) The light passes through a narrowband optical filter and is output to the seventh optical fiber 711.

Here, monitor signals for the amounts of light received by the first photoreceiver 713 and the second photoreceiver 710 are input to a control circuit 714, and based on these signals, the optical amplifier 5
02 gain is controlled. The control process is the same as in the first embodiment, but the spectrum of the light received by the second light receiver is different from the explanation in (effect), as shown in FIG. 2(b).
(when there is signal light) or the spectrum shown in FIG. 4(b) (when there is no signal light). However, even in this case, since the ratio of the monitor signal level of the second receiver to the monitor signal light level of the first receiver when there is no signal light is known in advance, if the ratio is greater than that, the signal light If the ratio is shown, it can be determined that there is no signal light. This is also because the reflected light level from the narrowband optical filter can be used as a reference level.

The features of this configuration are that there is generally no need to use an expensive optical circulator, and that the optical branching element for monitoring the reflected light from the narrow band optical filter and for monitoring the output light level from the optical amplifier is integrated into one optical branching element. Because it also serves as an element,
Even though an optical branching element is used for monitoring reflected light, the loss of the amplified signal light can be suppressed to a low level.

FIG. 8 shows a configuration diagram of a fourth embodiment of the present invention. The signal light that has passed through the first optical fiber 801 and entered the optical amplifier 802 is optically amplified and then transferred to the second optical fiber 803.
is output to. As shown in FIG. 2(b), this output light includes spontaneous emission light in addition to optically amplified signal light. The optically amplified signal light that entered the second optical fiber 803 enters the first terminal 821 of the optical isolator 804,
The signal is output from the second terminal 822 and is output to the third optical fiber 805. The direction of isolation of this optical isolator is such that the light incident from the first terminal 821 passes through the optical isolator, and the light traveling from the second terminal 822 to the first terminal 821 is not transmitted. Now, the light input to the third optical fiber 805 is input to the first terminal 831 of the optical branching element 806, and 90% of the light is output from the second terminal 832 to the fourth optical fiber 807. It is input to bandpass optical filter 816 . Note that the configuration of the narrow band optical filter 816 used here is the same as in the first embodiment, as shown in FIG.

Of the light input from the fourth optical fiber 807 to the narrow band optical filter 816, the spontaneous emission light component with the spectrum shown in FIG.
and is output to the fourth optical fiber 807 from which it came. This light is again transmitted from the second terminal 832 to the optical branching element 80.
6, 10% of the light is outputted from the fourth terminal, inputted into the sixth optical fiber 808, and received by the first optical receiver 809. Based on the received light amount, the spontaneous emission light amount of the optical amplifier 802 is monitored. Of the light input from the fourth optical fiber 807 to the narrowband optical filter 808, FIG. 2(c) (when there is signal light), FIG.
) (in the case where there is no signal light), the light having the spectrum shown in FIG. The output light to this fifth optical fiber 810 is
98% of it is output to the seventh optical fiber 812, and 2% is output to the eighth optical fiber 81.
3 is output. The output light to the eighth optical fiber 813 having the spectrum shown in FIG. 2(c) (when there is signal light) or FIG. 4(c) (when there is no signal light) is received by the second optical receiver 814. and amplified signal light (when there is a signal)
Alternatively, the light intensity level of the spontaneously emitted light (when there is no signal light) transmitted through the narrow band optical filter is monitored.

Here, monitor signals for the amount of light received by the first photoreceiver 809 and the second photoreceiver 814 are input to a control circuit 815, and based on these signals, the optical amplifier 8
02 gain is controlled. The control process is the same as in the first embodiment, and will be omitted here.

The feature of this configuration is that, like the third embodiment, there is no need to use an optical circulator, and there are two optical branching elements.
Although the optical branching element for monitoring the amplified signal light is placed after the narrowband optical filter, the monitor light contains almost no spontaneous emission light component, and the amplified signal light The optical power level can be easily monitored.

FIG. 9 shows a configuration diagram of a fifth embodiment of the present invention. The signal light that has passed through the first optical fiber 901 and entered the optical amplifier 902 is optically amplified and then transferred to the second optical fiber 903.
is output to. As shown in FIG. 2(b), this output light includes spontaneous emission light in addition to optically amplified signal light. The optically amplified signal light that entered the second optical fiber 903 enters the first terminal 921 of the optical isolator 904,
The signal is output from the second terminal 922 and is output to the third optical fiber 905. The direction of isolation of this optical isolator is such that first, light incident from the terminal 921 passes through the optical isolator, and light traveling from the second terminal 922 to the first terminal 921 does not pass through. Now, the light propagated through the third optical fiber 905 is input to the first terminal 931 of the narrow band optical filter 906. Of this input light, a spontaneous emission light component with a spectrum as shown in FIG. 907.

FIG. 10 shows details of the configuration of the narrowband optical filter 906. The narrowband optical filter is shown in Figure 3(a).
A dielectric multilayer filter 1001 having transmission/reflection characteristics as shown in (b) is attached to two first and second rod lenses 1002 and 1003 (both lengths are 1/4 pitch).
Furthermore, a third optical fiber 905 through which the light incident on the rod lens propagates, and fourth and fifth optical fibers 907 through which the output light from the narrow band optical filter 906 is input. Of the optical fibers 909, the third and fourth optical fibers are installed at symmetrical positions substantially parallel to the central axis of the first rod lens 1002, and the fifth optical fiber
The optical fiber 909 is approximately parallel to the central axis of the second rod lens 1003, and its tip is connected to the third optical fiber 905.
It is installed at a position where the light emitted from the lens forms an image. Therefore, the light incident from the third optical fiber 905 and reflected by the dielectric multilayer filter 1001 is transmitted to the fourth optical fiber 90.
Combined with 7. Now, the light input to the fourth optical fiber 907 is output to the first light receiver 908.

On the other hand, the light input from the first terminal 931 of the narrow band optical filter 906 and transmitted through the narrow band optical filter 906 is output from the third terminal 933 to the fifth optical fiber 909 . This output light has a spectrum shown in FIG. 2(c) (when there is signal light) or FIG. 4(c) (when there is no signal light). This light enters the first terminal 941 of the optical branching element 910, and 98% of it enters the second terminal 941.
2 to the sixth optical fiber 911, and becomes an output as an optical amplification device. The remaining 10% of light is sent to the optical branching element 91
The light is output from the third terminal 943 of No. 0, propagates through the seventh optical fiber 912, and is received by the second light receiver 913. As a result, the light intensity level of the amplified signal light (when there is signal light) or the spontaneously emitted light that has passed through the narrow band optical filter 906 (when there is no signal light) is monitored.

Here, monitor signals for the amount of light received by the first photoreceiver 908 and the second photoreceiver 913 are input to the control circuit 914, and based on these signals, the optical amplifier 9
02 gain is controlled. The control process is the same as in the first embodiment, and will be omitted here.

The feature of this configuration is that, like the third and fourth embodiments, there is no need to use an optical circulator, and even though no optical circulator is used, all the reflected light from the narrow band optical filter is used as monitor light. Since the optical branching element used in the second and third embodiments is not required before the narrowband optical filter, the attenuation of the optically amplified optical signal within the optical amplifier can be suppressed to a small level. This is the case.

The embodiments of the present invention have been described above. In the above embodiments, a dielectric multilayer filter is used as a component of the narrowband optical filter, but other narrowband optical filters such as a Fabry-Perot optical filter may be used. Further, although the branching ratio of the optical branching element is set to 1:9, 2:98, etc., it goes without saying that other ratios may be used. In addition, an optical fiber amplifier was used as an optical amplifier, but
Other optical amplifiers such as semiconductor optical amplifiers may also be used.

[0034]

According to the optical amplifier control method and optical amplifier device according to the present invention, it is possible to control the gain of the optical amplifier without superimposing a low frequency signal on the transmitted signal light.
There is no so-called chirping of the transmitted light wavelength due to modulation with a low frequency signal, and long-distance transmission becomes possible.

[Brief explanation of the drawing]

FIG. 1: Configuration diagram of the first embodiment of the present invention

[Fig. 2] Diagram for explaining the first to fifth embodiments

[Fig. 3] Diagram for explaining the first to fifth embodiments

[Figure 4]
Diagram for explaining the first to fifth embodiments

[Fig. 5] Configuration diagram of the second embodiment of the present invention

FIG. 6 is a detailed diagram of the configuration of the narrowband optical filter 507.

[Figure 7
] Configuration diagram of the third embodiment of the present invention

[Fig. 8] Configuration diagram of the fourth embodiment of the present invention

[Fig. 9] Configuration diagram of the fifth embodiment of the present invention

FIG. 10 is a detailed diagram of the configuration of narrowband optical filter 906.

[Explanation of symbols]

100 Optical amplification device 101 Optical amplifier 102 Input signal light 103 Optical amplifier output light 104 Narrowband optical filter 105 Reflected light 106 Light branching mirror 107 Photo receiver 108 Transmitted light 109 Light branching mirror 110 Branch light 111 Photo receiver 112 Output signal light 113 Control circuit 501 Optical fiber 502 Optical amplifier 503 Optical fiber 504 Optical circulator 506 Optical fiber 507 Narrowband optical filter 508 Optical fiber 509 Optical fiber 510 Photoreceiver 511 Optical branching element 512 Optical fiber 513 Optical fiber 514 Photoreceiver 515 Control circuit 521 First terminal 522 Second terminal 523 Third terminal 601 1/4 pitch rod lens 602 1/4 pitch rod lens 603 Dielectric band multilayer filter 701 Optical fiber 702 Optical amplifier 703 Optical fiber 704 Optical isolator 705 Optical fiber 706 Optical branching element 707 Optical fiber 708 Narrowband optical fiber 709 Optical fiber 710 Photoreceiver 711 Optical fiber 712 Optical fiber 713 Photoreceiver 714 Control circuit 721 First terminal 722 Second terminal 731 First terminal 732 Second terminal 733 Third terminal 734 Fourth terminal 801 Optical fiber 802 Optical amplifier 803 Optical fiber 804 Optical isolator 805 Optical fiber 806 Optical branching element 807 Optical fiber 808 Optical fiber 809 Photoreceiver 810 Optical fiber 811 Optical branching element 812 Optical fiber 813 Optical fiber 814 Photoreceiver 815 Control circuit 816 Narrowband filter 821 First terminal 822 Second terminal 831 First terminal 832 Second terminal 833 Third terminal 901 Optical fiber 902 Optical amplifier 903 Optical fiber 904 Optical isolator 905 Optical fiber 906 Narrowband optical fiber 907 Optical fiber 908 Photoreceiver 909 Optical fiber 910 Optical branching element 911 Optical fiber 912 Optical fiber 913 Photoreceiver 914 Control circuit 921 First terminal 922 Second terminal 931 First terminal 932 Second terminal 933 Third terminal 941 First terminal 942 Second terminal 943 Third terminal 1001 Dielectric band multilayer filter 1002 Rod lens 1003 Rod lens

Claims (5)

[Claims] 1. An optical amplification device including an optical amplifier and a narrowband optical filter connected after the optical amplifier and for removing spontaneous emission light output from the optical amplifier, wherein the light transmitted through the narrowband optical filter is An optical amplifier device comprising means for comparing the intensity of light reflected by the narrowband optical filter with the intensity of light reflected by the narrowband optical filter to control the gain of the optical amplifier. 2. A device having at least three terminals, wherein light input from the first terminal is output from the second terminal, and light input from the second terminal is output from the third terminal. a circulator; an optical amplifier having an output connected to a first terminal of the optical circulator; a narrowband optical filter having an input connected to a second terminal of the optical circulator; and an output light from the narrowband optical filter. and a control circuit that controls the gain of the optical amplifier using the output light from the third terminal of the optical circulator. 3. Light input from the first input/output terminal is output from the second and third input/output terminals, and the second
A light branching element through which light input from the input/output terminal is outputted from the first and fourth input/output terminals, and a first input/output terminal of the light branching element are connected in a direction in which the light is transmitted. an optical isolator, an optical amplifier connected to the front stage of the optical isolator, a narrowband optical filter connected to the second input/output terminal of the optical branching element, and a third input/output terminal of the optical branching element. and a control circuit that controls the gain of the optical amplifier using the output light from the fourth input/output terminal of the optical branching element. 4. An optical amplifier comprising an optical amplifier, an optical isolator connected to a downstream stage of the optical amplifier, first and second input/output terminals, and a monitor terminal for monitoring input light from the second input/output terminal. a first optical branching element, the first input/output terminal of which is connected to the output of the optical isolator;
a narrowband optical filter connected to a second input/output terminal of the optical branching element, and a monitor terminal for monitoring input light from the first and second input/output terminals and the first input/output terminal. ,
a second optical branching element whose first input/output terminal is connected to the output of the narrowband optical filter; and the optical amplifier using the output light from the monitor terminals of the first and second optical branching elements. An optical amplification device comprising: a control circuit for controlling the gain of the optical amplifier. 5. An optical amplifier, an optical isolator connected after the optical amplifier, and an optical isolator placed after the optical isolator, in which the reflected light of the light incident thereon follows an optical path different from the original optical path. The gain of the optical amplifier is controlled using a narrowband optical filter installed at an angle with respect to the incident optical axis, and output light from the narrowband filter and reflected light from the narrowband optical filter so that An optical amplification device comprising: a control circuit.